NAME

LIBRARY

SYNOPSIS

#include<stdio.h>FILE*stdin;
FILE*stdout;
FILE*stderr;
Note: The current implementation does not allow these variables to be
evaluated at C compile/link time. That is, a runtime calculation must be
performed, such as:
#include <stdio.h>
static FILE *var;
int main() {
var = stdout;
}

DESCRIPTION

The standard I/O library provides a simple and efficient buffered stream
I/O interface. Input and output is mapped into logical data streams and
the physical I/O characteristics are concealed. The functions and macros
are listed below; more information is available from the individual man
pages.
A stream is associated with an external file (which may be a physical
device) by opening a file, which may involve creating a new file. Creat-
ing an existing file causes its former contents to be discarded. If a
file can support positioning requests (such as a disk file, as opposed to
a terminal) then a filepositionindicator associated with the stream is
positioned at the start of the file (byte zero), unless the file is
opened with append mode. If append mode is used, the position indicator
will be placed at the end-of-file. The position indicator is maintained
by subsequent reads, writes and positioning requests. All input occurs
as if the characters were read by successive calls to the fgetc(3) func-
tion; all output takes place as if all characters were written by succes-
sive calls to the fputc(3) function.
A file is disassociated from a stream by closing the file. Output
streams are flushed (any unwritten buffer contents are transferred to the
host environment) before the stream is disassociated from the file. The
value of a pointer to a FILE object is indeterminate (garbage) after a
file is closed.
A file may be subsequently reopened, by the same or another program exe-
cution, and its contents reclaimed or modified (if it can be repositioned
at the start). If the main function returns to its original caller, or
the exit(3) function is called, all open files are closed (hence all out-
put streams are flushed) before program termination. Other methods of
program termination may not close files properly and hence buffered out-
put may be lost. In particular, _exit(2) does not flush stdio files.
Neither does an exit due to a signal. Buffers are flushed by abort(3) as
required by POSIX, although previous implementations did not.
This implementation makes no distinction between ``text'' and ``binary''
streams. In effect, all streams are binary. No translation is performed
and no extra padding appears on any stream.
At program startup, three streams are predefined and need not be opened
explicitly:
ostandardinput (for reading conventional input),
ostandardoutput (for writing conventional output), and
ostandarderror (for writing diagnostic output).
These streams are abbreviated stdin, stdout and stderr. Initially, the
standard error stream is unbuffered; the standard input and output
streams are fully buffered if and only if the streams do not refer to an
interactive or ``terminal'' device, as determined by the isatty(3) func-
tion. In fact, all freshly-opened streams that refer to terminal devices
default to line buffering, and pending output to such streams is written
automatically whenever such an input stream is read. Note that this
applies only to ``true reads''; if the read request can be satisfied by
existing buffered data, no automatic flush will occur. In these cases,
or when a large amount of computation is done after printing part of a
line on an output terminal, it is necessary to fflush(3) the standard
output before going off and computing so that the output will appear.
Alternatively, these defaults may be modified via the setvbuf(3) func-
tion.
The stdio library is a part of the library libc and routines are automat-
ically loaded as needed by the C compiler. The SYNOPSIS sections of the
following manual pages indicate which include files are to be used, what
the compiler declaration for the function looks like and which external
variables are of interest.
The following are defined as macros; these names may not be re-used with-
out first removing their current definitions with #undef: BUFSIZ, EOF,
FILENAME_MAX, FOPEN_MAX, L_ctermid, L_cuserid, L_tmpnam, NULL, P_tmpdir,
SEEK_CUR, SEEK_END, SEEK_SET, TMP_MAX, clearerr, clearerr_unlocked, feof,
feof_unlocked, ferror, ferror_unlocked, fileno, fileno_unlocked, fropen,
fwopen, getc, getc_unlocked, getchar, getchar_unlocked, putc,
putc_unlocked, putchar, putchar_unlocked, stderr, stdin and stdout.
Function versions of the macro functions clearerr, clearerr_unlocked,
feof, feof_unlocked, ferror, ferror_unlocked, fileno, fileno_unlocked,
getc, getc_unlocked, getchar, getchar_unlocked, putc, putc_unlocked,
putchar, and putchar_unlocked exist and will be used if the macro defini-
tions are explicitly removed.

LEGACY SYNOPSIS

The -D_NONSTD_SOURCE flag can be used to allow stdin, stdout, and/or
stderr to be evaluated at compile/link time, as:
#include <stdio.h>
static FILE *var = stdout;